Solid high-energy compositions, such as propellants, explosives, gasifiers, or the like, comprise solid particulates, such as fuel particulates and/or oxidizer particulates, dispersed and immobilized throughout a binder matrix comprising an elastomeric polymer.
Binders previously used in composite solid propellant formulations have generally been non-energetic polymers such as polycaprolactones, polyethyleneglycols or polybutadienes. Since about 1950 there has been a considerable need to develop energetic binders with satisfactory mechanical properties in order to provide safer binders at higher energy levels and to increase the energy level or specific impulse in a propellant formulation. For the most part only nitrocellulose has found usefulness as an energetic polymer binder. However, nitrocellulose suffers from undesirable mechanical properties. Alternatively, it has been proposed to employ conventional non-energetic polymer binders in combination with energetic plasticizers such as for example, nitroglycerine, butanetriol trinitrate, and trimethylolethane trinitrate. It has also been suggested that the energetic polymer nitrocellulose be employed with either non-energetic or energetic plasticizers in an attempt to improve mechanical properties. However, none of these proposals has led to fully acceptable energetic binder formulations. Furthermore, there are many occasions when the use of plasticizers is undesirable or its use is not possible, such as when "clean" space motor/gas generator propellants or "clean" large launch vehicle propellants are required.
Thus, there has been a continuing need for energetic polymers to be available for use in formulating solid high-energy compositions, such as propellants, explosives, gasifiers and the like. In this regard much recent work has centered on attempts to produce acceptable energetic polymers of glycidyl azide polymer and poly(oxytanes). A problem with elastomeric binders formed from poly(oxytanes) is their tendency to have mechanical characteristics less than that which would be desirable for a high-energy composition, particularly for a rocket motor propellant. It is especially difficult to provide poly(oxytane) binders having adequate stress capabilities. On the other hand glycidyl azide polymer is synthesized by first polymerizing epichlorohydrin to poly(epichlorohydrin) which is then converted to glycidyl azide polymer by reaction with sodium azide in dimethylsulfoxide. Beside the lack of a simple synthesis process, the production of glycidyl azide polymer requires relatively expensive reagents.
Since the early 1950's poly(glycidyl nitrate), hereinafter referred to as PGN, has been known and recognized as an energetic prepolymer. The initial work on PGN was done by Thelan et al. at the Naval Ordnance Test Station (NOTS, now Naval Weapons Center, NWC). They studied the polymerization of glycidyl nitrate by a variety of Lewis Acid catalysts with most of the work centering on the use of stannic chloride as a catalyst. No propellants were prepared by the NOTS workers and they noted that one drawback to their synthesis was the laborious purification procedure.
PGN AND PGN propellants were next examined at the Jet Propulsion Laboratory (JPL) by Ingnam and Nichols and at Aerojet General Corporation by Shookhoff and Klotz. The JPL workers found that PGN made using boron trifluoride etherate was low in both functionality (i.e. &lt;2) and molecular weight (MW=1500) and therefore polyurethane propellants made from this PGN had poor mechanical properties. Similar observations were made by the Aerojet workers. In summary, it has long been recognized that PGN would be an excellent energetic polymer but until now a method of synthesis could not be found that would produce nearly difunctional material with acceptable hydroxyl equivalent weights.
It is therefore desirable and an object of this invention that a process for the production of PGN be provided that would produce nearly difunctional material with acceptable hydroxyl equivalent weights. A further object of this invention is to provide a process for the production of PGN that produces "propellant quality" PGN. A still further object of this invention is to provide a process to produce PGN having a functionality of nearly 2.0 and a hydroxyl equivalent weight of about 1000-1700 or more, preferably about 1200 to 1600. It is yet another object of this invention to provide a process for producing PGN that has present greatly reduced amounts of cylic oligomer, that is about 2-5% by weight or less.